1. Field of the Invention
The present disclosure is directed to systems and methods for generating high volumes of foam and, more particularly, to systems and methods for foam generation that are capable of advantageously producing high volume, low pressure foam. The disclosed systems and methods for foam generation are efficient and useful in a variety of conditions and circumstances.
2. Background Art
Compressed air foam systems provide a powerful tool for many applications. Many traditional compressed air foam systems combine water, foam solution, and air from a compressor and then pump the mixture through a hose, thus creating compressed air foam. A traditional system for generating foam includes a water pump, water tank, foam injection pump, air compressor, a mixing chamber to mix water, foam and air, and controls necessary for mixing the three agents while maintaining the pressure. The mixture of air, water and foam may then be delivered through a hose.
Some of the shortcomings associated with traditional systems and methods for generating foam are illustrated by the following discussion. A water pump used on a firefighting vehicle is usually capable of producing water pressures from about 250 to about 400 psi and delivering about 40 to 60 gallons per minute (gpm) of water. Presently available air compressors are usually capable of delivering compressed air at about 30 to about 200 cubic feet per minute (cfm) at about 150 psi, with a maximum of 200 psi achieved by high-performance units. In conventional foam generation systems, the air, water and foam must all operate at the same pressure, e.g., at the firetruck or other foam generation location, and pressure control systems must be provided to ensure that the pressures are appropriately equalized. For example, if the water pressure is too high, mixing of with the compressed air cannot be effected. Thus, when traditional systems for generating foam are used with the presently available water pumps and air compressors, the limited compressor discharge pressure and volume capacity are limiting factors.
More particularly, the limited capabilities of the air compressor restrict the overall pressure that the entire system is capable of delivering, i.e., conventional foam generation systems may be limited to about 200 psi maximum. The flow of foam encounters significant friction loss when transmitted through hoses according to conventional foam generation systems. Indeed, these friction losses can significantly impede or back up the flow of foam in conventional systems. Because conventional systems are limited to outlet pressures of 150–200 psi based on the available air pressure, the potential utility of foam generation systems is significantly restricted or completely defeated in a variety of important fields and applications.
Once the water/foam and high pressure air are combined, e.g., in a compressed air system positioned on a firetruck, the high pressure foam must be transported to the desired target. Such foam transport is generally accomplished by way of a conventional fire hose that ranges in diameter from 1″ to 2½″. Conventional compressed air foam systems are more effective when larger diameter fire hoses are employed, but have limited potential for use with smaller diameter hoses, e.g., ⅝″ to 1″ hoses. These smaller diameter fire hoses are widely employed for brush fire and wildland/urban interface applications.
The following examples further illustrate the significant limitations associated with conventional compressed air foam systems. In fighting wildland and/or brush fires, hoses of one foot diameter are typically employed, and such hoses generally stretch about 300 feet from the truck to the fire nozzle. Fire fighting systems generally deliver a flow rate of 60 gpm from the truck to the nozzle. The friction loss at 60 gpm for a 1′ diameter rubber hose is approximately 276 psi. If a “high quality” compressor delivers air to the foam generation system at a pressure of 200 psi, the system is still 76 psi below the pressure required to overcome the friction forces of the hose, without even taking into account the approximately 100 psi required at the nozzle to effect the desired discharge. Even if the flow rate were reduced to 40 gpm, the friction loss for a 1′ diameter rubber hose would be approximately 132 psi. Thus, at best, only 70 psi would be available at the nozzle to effect foam discharge, which falls short of the desired 100 psi.
Various systems for foam generation have been provided in the patent literature. For example, U.S. Pat. No. 3,393,745 to Durstewitz describes fire-fighting foam generating apparatus and, more particularly an apparatus which includes a centrifugal fan, a cylindrical foam forming net surrounding the fan, a source of foam producing solution under pressure, and a plurality of reaction nozzles mounted on the fan rotor for spraying the solution onto the net and for driving the fan rotor by the reaction forces thus produced to pump air outwardly through the net to generate high expansion foam. Another system for foam generation is provided in the U.S. Pat. No. 3,424,250 to Thomas, which describes an apparatus for entraining air in a mixture of water and detergent compound to form a foam and then entraining further air in the foam to provide a high expansion foam for use in fire fighting.
U.S. Pat. No. 3,607,779 to King et al. describes a tubular housing with a rear inlet and a front end outlet that has a foraminous cover over its front end. A shaft extends lengthwise of the inside of the housing and is rotatably supported. It is driven by a water turbine on its front end, the turbine having an inlet for water under pressure and a central front outlet that delivers the water to a forwardly directed nozzle connected to the turbine. Rigidly mounted on the shaft behind the turbine is a fan for blowing air through the housing from back to front. Also mounted on the shaft is a pump for delivering foaming solution to the rear end of the nozzle to mix with the water from the turbine outlet.
U.S. Pat. No. 3,780,812 to Lambert describes a fire protection method and apparatus for generating a high expansion foam. The method includes fluidizing the foams by wetting. The apparatus includes a housing having a source of foam solution under pressure and a source of water under pressure. The housing includes a fan and a perforated member. The fan is positioned in the housing to provide air flow across the perforated member which is wetted by the foam solution to produce high expansion foam bubbles. The fan is driven by a plurality of nozzles mounted both for discharging the water under pressure and for wetting the foam bubbles.
U.S. Pat. No. 5,337,830 to Bowman describes a system for generating fire-fighting foam whereby a foam-forming chemical is mixed with water and air to form foam. The foam is pressurized preferably by the provision of pressurized air to force the foam out of a duct within which the foam is formed and to direct the foam at the seat of the fire or to the site to be protected against fire. A metal mesh is rotatable and preferably helical with respect to the direction of travel of the foam which acts as a catalytic agent and helps to clear foam from the duct within which the foam forms.
U.S. Pat. No. 5,787,989 to Elmenhorst describes a fan casing and a fan which are operated by a reaction jet motor. The reaction jet motor has nozzles and is connected to a liquid under pressure, usually water with a foaming agent added. When the liquid is sprayed from the nozzles, the reaction forces will operate the fan. The nozzles are designed in such a manner that they generate a cohesive and compact jet with high thrust. A grid is located between the nozzles and the foam net for atomization and dispersion of the liquid. The air blows the liquid through the foam net, thus generating fire-fighting foam.
U.S. Pat. No. 4,595,142 to Kawaharazuka et al. describes a blower/spray device which includes a tank containing a liquid chemical agent that is removably mounted on a main body, an air extracting line secured to the upper portion main body, and an air introducing member secured to the bottom wall of the tank and aligned with the outlet of the air extracting line. The blower is driven by an internal combustion engine.
Although the prior art systems and methods described above (and other presently used systems and methods for foam generation) may result in adequate foam generation for the specific and limited purposes for which they are used, these prior art systems and methods fail to generate foam in a way and of a quality for widespread and effective use.
Thus, there remains a need for systems and methods for foam generation that are capable of producing relatively high volumes of foam that can be effectively delivered when and where needed. Further, there remains a need for systems and methods for foam generation that overcome the pressure-related limitations of conventional foam generation systems.